Currently the code queries the current msc then tries to approximate the
value of the next msc satisfing the modulus 2 for when to wait. This
introduces some instability as the msc may tick over during the
roundtrip leading to a 32ms wait instead of a 16ms wait. This happens
often enough to cause jerky animations, and affect gnome-shell-perf-tool.
A simpler solution is just use a single roundtrip by using WaitForMsc to
ask the driver to compute the next vblank itself.
Cc: Owen W. Taylor <otaylor@fishsoup.net>
Cc: Robert Bragg <robert@linux.intel.com>
Reviewed-by: Robert Bragg <robert@sixbynine.org>
5ccd2825c7